Variable transmission mechanism



Aug. 6, 1940..

H. K. HERRICK VARIABLE TRANSMISSION MECHANISM Filed Aug. 3. 1938 I N V EN T 0 R Homer Herr/ck BY 4444.)

Can 770/ Mecham's/n ATTORNEY Patented Aug. 6, 1940 UNITE-DflS'TATES rareN OFFICE VARIABLE TRANSMISSION MECHANISM Homer "K. Herrick; South'I'asadena, Galif. Application August 3, 193$,-erial No. 222,846

7 Claims.

-. This invention relates to a mechanism for transmitting motion from adriving shaft to a driven shaft; and especiallyto a device of thischaracter that maybe controlled-to vary the ratio :ofithespeeds betweenthe driving and driven ele- .ments; n

.In.one:type of mechanism adapted to-perform this function, .it has beencommon to provide a .set ofwheels or gears arranged to add or subtract'10 their motions, as by-differential gear arrangemerits. Suchdevices,how-ever, require considerable space. Also, it is necessary toprovideadvditionalelements to render it possible to arrange the driving .anddrivenshafts coaxially.

;:,,1=5 It is one of the objects of this invention-topmvide .a mechanismof this generalcharacter that .is .compactand yet rthatran be arrangedfor coaxial. drive. 1

This result is obtained by providing adriving lconnectionbetweentwoconcentric wheelsyone insidethe othenthatpermits these wheels to'bequite closely.nested;.together, and yet-permits a large ratio variation;It is accordingly another objectof this invention to make it possible,-by Y 25 theaid of this interconnection, to provide a oom'-pact,..elfective. drive .at, ratios variable within wide limits;

1By so arrangingthe interconnecting member as afiexible loop, .such asva sprocket. chain, the

.30 ,highly desirable compactness can be readilyattained. It is.accordingly another object-f this invention .to make it possibleto'utilize such a flexible. member in. a differential gear mechanism ofthis character.i

435 This inventionpossesses many. other advantages,,and has otherobjects.which may be made more easily apparent :from-a consideration of oneembodiment. ofthe invention. .For this purposel here is shown .aform inthe drawing. accom- 3 panying and forming part of r the .present:specification. This form .yvillnow be described in detail,illustrating. the. general. principles ofthe invention; but it istonberunderstood that this detailed descriptionv is not to be taken in alimiting sense, since the scope of this invention .is .best

defined by the appendedclaims.

Referring to the drawing: v Figure 1 is a longitudinal-sectional view ofan apparatus incorporating the invention;

:50 Figure} is across section taken along plane Z-2 of Figure l, aportion of the flexible connectionbeing shown in section; and

.Figure 3 is a. fragmentary sectional view, taken ,along plane 3-.-3.ofFigure 1.

.55 The transmission mechanismisshown as having an axis l. The shaft '2andthe shaft 3, which rnay comprise respectively a driving and drivenshaft, or vice versa, are coaxial with the axis I. If we assume thatshaft 2 is the driving shaft, --it may be appropriately connected to be,5

.driven by a source of power and supported adjacent one end thereof asin the journal bearing structure 4. The driven shaft 3 may be connected'to any appropriate load (not shown).

In order to transmit motion from one shaft to ,10 the other at avariable ratio, use is made of a ,pair of concentric wheel members, bothof them having anaxis coincident with axis I Thus fixed toshaft 2 as bythe aid of the key 5, is an inner wheel member 5. This wheel member 6has e hub lior providing a sui liciently large contacting surfacebetween the wheel and the shaft 2.

Arranged concentrically with the wheel member 6 is another Wheel member8. The outer periphery of the wheeljBis shown as in contact with theinner surface ID of a housing 9 and abutting a shoulder I l thereon. Thewheel member 8 may be securely attached within the housing member ber;.I,6 rabbetted into the lefthand edge of the housing .9 and also rotatably -moun ted upon a .rnernber l1. concentric with'the shaft 2.

' The housing 9, is intended to be placed into driving relation withthe'driven shaft 3, as by a coupling. For this purpose it mayv beprovided .with a plurality of pins |8.arranged annularly aboutthe axis Iand adapted to engage in corresponding apertures I79 formed in acoupling memberzfl. This coupling member is shown as 4 keyed to thedriven shaft 3, as by the aid ofthe By providing concentric wheelmembers 6 and 8 in compact arrangement, the drive between the shafts 2and 3 ismadelcoaxial, and little space is taken up by .the transmissionmechanism which is .substantiallyentirely enclosed in the rotary housing.9.

In order to eifect a driving relation between ,thewhe el members, useis'made of a connection I capable of transmitting rotary forces from onewheel to the other.

In order to transmit the torque from one to the other, the membersfi and8 are shownrespectively as provided with. ex-

t nal tee h. an interna teeth .23. .The. con- .1 5

nection between the Wheels may be in the form of a rigid ring meshingwith both sets of teeth; but in order tomake it possible to reduce theover-all diameter of the apparatus, use is made of a flexible membersuch as a sprocket chain 24. This sprocket chain is shown as partiallybroken away in Figure 2. The sprocket pin bushings 25 through which passthe pins 33 that join the links in the chain, are shown as wide enoughto engage the wide teeth 23 of the outer wheel member 8. The chain 24encompasses the inner sprocket wheel 6, and is urged or maintained inoperative relation with the teeth 23, in spite of the fact that themember 24 is flexible. This is accomplished by an eccentric mechanism.

Thus mounted for free angular motion about shaft 2 is the hub Elcarrying an eccentric 26. Mounted for free rotation on the eccentric isthe ring 21. This ring 21 has a flange 28 adapted to engage the bushingsor rollers 25. The ring 2'! is arranged closely adjacent the sprocketwheel 6 for this purpose. By an inspection of Figure 2 it is seen thatthe eccentricity of the eccentric mechanism is such that the sprocketchain is kept in proper taut operative relation with both the innerwheel teeth 22 and the outer wheel teeth 23.

Rotation of either shaft 2 or 3 in either direction will transmit arotational force through the eccentric mechanism and the chain 24 to theother shaft. It may readily be demonstrated that by appropriate controlof the angular motion of the eccentric 25 about axis I, the ratio oftransmission may be correspondingly controlled. Thus in Figure 2,'if weassume that there are a, teeth 22 on wheel 6 and that there are c teeth23 in the outer wheel 8, it may be readily demonstrated that for theshaft 3 to be rotated in unison with shaft 2, the eccentric mechanismmust be rotated about axis I in unison with shaft 2. The member 24 thenserves merely as a clutching member between shafts 2 and 3.

If the eccentric mechanism is maintained against any angular motion, theratio of transmission from shaft 2 to shaft 3 is the same as the ratioof the teeth; that is, the wheel 8 is rotated in the ratio of withrespect to the rate of rotation of the inner "where A is the angularmotion of shaft 2, and B is the angular motion of eccentric 24. Now ifit is desired to bring the rotation of the driven shaft 3 to Zero, thiscan be accomplished by imparting to the eccentric mechanism an angularmotion equal to and in a direction reverse tothat of the rotation ofshaft 2. This follows immediately from an application of the generalformula given above. To obtain other ratios of transmission, the angularmotion B of the eccentric mechanism may be correspondingly controlled.In general, the larger the angular motion B is in a positive direction,the larger the resultant angular motion of shaft 3 is in this positivedirection.

.The'means for controlling the rotation'of the eccentric mechanism isillustrated in Figure 1 as comprising a sprocket wheel 29 keyed to theeccentric hub l1 and joined as by a sprocket chain 30 to a sprocketwheel 3| mounted on the control mechanism 32. This control mechanism maybe a brake or source of motion, such as a motor, for determining theangular motion of the eccentric mechanism.

The transmission of power between shafts 2 and 3 may. of course be thereverse of that specifled; that is, the shaft 3 may be the driving shaftand the shaft 2 maybe the driven shaft.

What is claimed is:

1. In a transmission mechanism, coaxial driving and driven shafts, apair of coaxial inner and outer sprocket wheels, the inner wheel beingfixed on one shaft, a housing surrounding said one shaft and rotatablysupported thereon, the outer wheel being carried by said housing, acoupling between the housing and the other shaft, a sprocket chainpassing around the inner wheel, and means urging said chain into drivingc0nnection with the outer wheel.

2. In a transmission mechanism, coaxial driving and driven shafts, apair of coaxial inner and outer wheel members, the inner wheel memberbeing fixed on one shaft, a housing surrounding said one shaft androtatably supported thereon, the outer wheel member being carried bysaid housing, a coupling between the housing and the other shaft, aflexible loop connection passing around the inner wheel and in drivingrelation thereto, and means urging said connection into driving relationwith the outer Wheel member.

3. In a transmission mechanism, coaxial driving and driven shafts, apair of coaxial inner and outer wheel members, the inner wheel memberbeing fixed on one shaft, a housing surrounding saidone shaft androtatably supported thereon,

the outer wheel member being carried by said housing, a coupling betweenthe housing and the other shaft, a flexible loop connection passingaround the inner wheel and'in driving relation thereto, an eccentric,mechanism mounted for angularvmovement about thecommon axis of theshafts forurging said loop connection into driving relation with theouter wheel member.

4. In a transmission mechanism, an inner and an outer sprocket wheel,said wheels being coaxial, the inner wheel having external teeth and theouter wheel having internal teeth, a chain in driving engagementwithboth wheels, and an eccentric. mechanism having an axis of motioncoaxial with the sprocket wheels for maintaining the chain in suchdriving engagement, said eccentric mechanism having a surface engagingthe chain in tandem with the chain engaging surfaces of the innersprocket wheel.

5. In a transmission mechanism, an inner and an outer sprocket wheel,said wheels beingcoaxial, the inner wheel having external teeth and theouter wheel having internal teeth, a chain in driving engagement withboth wheels, and an surfaceas well as the teeth of the inner sprocket"wheel. I

6. In a transmission mechanism, an inner and an outer sprocket wheel,said wheels being coaxial, the inner wheel having external teeth and theouter wheel having internal teeth, a. chain in driving engagement withboth wheels, and an eccentric mechanism having an axis of motion coaxialwith the sprocket wheels for maintaining the chain in such drivingengagement, the teeth on said outer sprocket being substantially widerthan the teeth on the inner sprocket wheel.

7. In a transmission mechanism, an inner and. an outer sprocket wheel,said wheels being oo- 0 axial, the inner wheel having external teethand.

the outer wheel having internal teeth, a chain in driving engagementwith both wheels, and an eccentric mechanism having an axis of motioncoaxial with the sprocket wheels for maintaining the-chain in suchdriving engagement, said eccentric mechanism having a surface engagingthe chain in tandem with the chain engaging surfaces of one of saidsprocket wheels.

